Drop-frame timecode is a way of counting frames at 29.97 or 59.94 fps so the timecode matches real clock time. No video frames are lost; instead, two frame numbers are skipped at the start of every minute except every tenth minute. Use it for US broadcast at 29.97; use non-drop for everything else.
When colour television arrived in the US, the frame rate changed from 30 to 29.97 frames per second for technical reasons. Timecode still counted 30 frame numbers per second, so after an hour the timecode read 3.6 seconds behind real time. For broadcasters scheduling programmes to the second, that mattered. Drop-frame timecode fixes the counting so an hour of timecode is an hour of clock time.
No pictures are dropped. Only the labels are. At the start of every minute, frame numbers 00 and 01 are skipped, so the count goes from 00:00:59:29 straight to 00:01:00:02. That happens every minute except minutes 00, 10, 20, 30, 40 and 50. Over an hour, 108 frame numbers are skipped, which is exactly the 3.6 seconds needed to stay in step with the clock.
Drop-frame timecode is usually written with a semicolon before the frames, or between all fields: 01:00:00;00. Non-drop uses colons throughout: 01:00:00:00. Cameras, recorders and editing software show the same convention, which is a quick way to check what a clip is using.
Camera, sound recorder and slate must agree not only on frame rate but also on drop or non-drop. If the sound recorder runs 29.97 drop and the camera 29.97 non-drop, the timecode will match at the start of the day and then disagree by a few frames every minute, and automatic syncing in the edit will be wrong. Check the setting when you jam, and write it on the camera report.
True-Slate handles drop frame properly and offers non-drop for every rate, so the timecode on your slate reads the same as the recorder it is jammed to.
No. Every frame of picture is kept. Only the frame numbers 00 and 01 are skipped at most minute changes, so the timecode stays in step with real time.
No. 25 fps is an exact rate, so its timecode already matches clock time. Drop frame only applies to 29.97 and 59.94 fps.
No. 23.976 fps always uses non-drop timecode, even though it runs slightly slower than 24.
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